Brachydactyly type D
|Brachydactyly type D|
|Child's thumbs with unilateral brachydactyly type D (with bitten nails giving the shortness a more extreme appearance than normally-treated nails)|
Stub thumb is a condition clinically recognised by a thumb being relatively short and round with an accompanying wide nail bed as the distal phalanx of affected thumbs is approximately two-thirds of full-length thumbs. Classified as brachydactyly type D, this skeletal variation is associated with the HOXD13 gene.
Stub thumbs are medically classified as brachydactyly type D (BDD) alias brachymegalodactylism. Coined by R.A. Hefner in 1924, 'stub thumb' is a scientifically preferred term used to identify brachydactyly type D. Stub thumbs have also been called murderer's thumb (allegedly among fortune tellers), bohemian thumb, and potter's thumb.
Brachydactyly type D is a skeletal condition allegedly caused by a 'partial fusion or premature closing of the epiphysis with the distal phalanx of the thumb', according to Goodman et alia (1965). J.K. Breithenbecher (1923) found that distal phalanges of stub thumbs were one-half the length of full-length thumbs, while R.M. Stecher (1957) claimed that it be approximately two-thirds. The condition may either be unilateral (affecting one thumb) or bilateral (affecting both).
A genetic trait, brachydactyly type D exhibits autosomal dominance and is commonly developed or inherited independently of other hereditary traits. The condition is associated with the HOXD13 gene, which is central in digital formation and growth.
A 1965 scientific study in Israel found that 3.05% of Israeli Arabs had one or two stub thumbs, compared with 1.57% among Ashkenazi as well as non-Ashkenazi Jews. However, as the survey's Arab test persons were mainly recruited from a handful of large and closely related clans living in a particular village, said percentage should be 'considered with some reservation', according to Goodman et alia (1965). Stub thumbs are also relatively common in Japan.
- GOODMAN RM; ADAM A; SHEBA C (1965). "A Genetic Study of Stub Thumbs Among Various Ethnic Groups in Israel". Journal of Medical Genetics. 2 (2): 116–21. PMC 1012845. PMID 14295653.
- McKusick, Victor A. 'Brachydactyly, Type D; BDD'. Online Mendelian Inheritance in Man. Retrieved on 2 May 2018. https://omim.org/entry/113200
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